The head portion of a ring wrench usually has an inner shape and size complementary to that of a typically hexagonal or square fastener head. The head of such a wrench has an inner surface which surrounds the fastener head with only a small amount of play between the inner surface of the wrench and the fastener head. As torque is applied to the wrench the torque is transmitted to the fastener head to turn the fastener in the appropriate direction.
Ring type wrenches are preferably to open jaw type wrenches because the torque applied to the wrench is transmitted to the fastener via a much larger contact area and the ring head of the wrench if closed can transmit far greater torque without harmful distortion of the fastener head and less chance of the wrench slipping off the fastener. Ring wrenches are however made to fit complementary fastener head sizes. Even if the inner ring wrench head surface is appropriately shaped only a small variation in size is possible between fastener head and the inner ring wrench head surface. Accordingly, wrenches are normally supplied in sets, for example a set of wrenches capable of use on the most common fastener sizes of say 10–19 mm would consist of 10 different wrench head sizes as well as the near equivalent imperial or metric sizes would consist of a further 5 Whitworth or B.S.P. sizes and 8-Inch A/F sizes.
Good quality wrench sets are quite easy to obtain and in use individually selected ones of the sets are found as necessary and used with the appropriately sized head of a fastener. When a fastener of another size is used the first wrench is discarded and another appropriately sized wrench is used. When a number of the wrenches are being used there is a tendency for the user to mislay a wrench size thereby extending the time and hence cost of completing a particular work task.
It is an object of the present invention to substantially alleviate the above mentioned disadvantages.